The PLCO Trial was designed as a large-scale randomized trial to investigate whether selected screening tests for cancers of the prostate, lung, colon, and ovaries lead to a reduction in mortality from these cancers. Approximately 155,000 women and men aged 55 to74 were enrolled in PLCO between 1992 and 2001. Participants were randomized into two arms, with intervention-arm participants receiving a series of six annual examinations to screen for prostate cancer, lung cancer, colorectal cancer, and ovarian cancer, and comparison-arm participants receiving routine health care from their health providers. Participants completed a risk factor questionnaire at baseline and a supplemental questionnaire in 2006. Another questionnaire (the Medical Use Questionnaire), designed to collect information on basic lifestyle factors and medication use, was mailed to PLCO participants in the first half of 2013. Questionnaires were completed and returned by approximately 56,000 participants. The questionnaires were designed to allow data entry using electronic scanning methods and character recognition software. The participant responses have been computerized and are currently undergoing data entry quality control checks at the PLCO Central Data Collection Center